Lens systems generate distortions. One of the most visible distortions in today's medium cost camera products is a radial distortion. The radial distortion is generated in camera systems by a non-homogeneous transversal magnification on the whole surface of the lens, but is a function of the off-axis distance.
The radial distortion is a non-linear distortion that manifests itself in the image by a radial displacement of the image points from the center of the distortion. The radial distortion is more commonly called a barrel distortion or a pincushion distortion depending on the direction of the radial distortion. The radial distortion properties, such as a distortion effect and a center of distortion, depend on the optical characteristics of the lens system, which may change for example as a result of focusing or zooming.
FIGS. 1a through 1d, illustrate different visible effects of the radial distortion on a grid test image and showing: a) a non-distorted image, b) a distorted image with the barrel distortion, c) a distorted image with the pincushion distortion and d) a distorted image with a combined barrel and pincushion distortion.